On Aquatic Carnworous Coleoptera or Dytiscide. 205 
large size in Meladema. In the Agabini and some of the neighbouring genera, the 
clypeal depressions appear to be entirely wanting, but on a careful examination of 
‘Dytiscus bipustulatus it will be seen that the front of the clypeus appears to be 
provided with a fine margin, and on looking at other species of the genus (Agabus) 
it will be seen that the depression causing the margin arises from the extension in 
the transverse direction of the clypeal depressions. 
The clypeus or epistoma is usually of a paler colour than the part of the head 
behind it, this is displayed in a very marked manner by the species of the genus 
Dytiscus, where the clypeus is yellow, and the front of the epicranium nearly black ; 
the darker colour of the epicranium frequently extends more or less on to the 
clypeus, so as to leave the anterior portion of this latter paler than the posterior 
part, but it is only very rarely indeed that the anterior portion of the clypeus is 
quite black in colour. 
The upper surface of the head shows no trace of any other suture besides the one 
existing between the epicranium and clypeus; the transverse suture between the 
epicranium and protocranium which Is very strongly marked in most of the Carabidee 
(in the natural condition concealed by the pronotum) being completely absent. 
The front of the epicranium on each side bears a well-marked irregular depression 
or fovea, which is occasionally more or Jess distinctly divided into two depressions 
placed one before the other (Meladema) ; these frontal foveze are entirely absent 
in the Noterides, and are only very indefinitely present in Hyphydrus, and some 
other Hydroporides, and are very much effaced in many members of the family 
having a very smooth and polished surface, such as the Hydaticides and Laccophilini ; 
these foveze are more punctate than the rest of the upper surface, and carry some 
very fine and short depressed hairs. The large eyes encroach on the upper surface 
of the epicranium, and their inner edge is usually limited by a more or less punctate 
depression. The vertex, or portion of the epicranium behind the eyes is much 
broader than the front, and is covered at the sides by the angles of the prothorax ; 
thus, the eyes notwithstanding their large size are not prominent, and the breadth 
of the head behind the eyes is as great (or very nearly as great) as it is across the 
eyes, this being contrary to what exists in the Carabidee, where the greatest breadth 
of the upper surface lies on a line drawn between the convex portions of the two 
eyes; there is no trace of any constriction behind the eyes. In the Colymbetides 
the surface of the head, when dark in colour, is usually marked by two more or less 
definite paler spots placed between the eyes, these frequently become united into 
one, and in Dytiscus are not only united, but placed so as to form an angular mark 
on the middle of the head; and in the Hydaticides, the head is usually pale but 
with dark vertex, and angular dark marks in front, of variable extension according 
to the species examined. | 
The antenna is inserted more or less conspicuously on the undersurface of the 
head ; the anterior angle of the epicranium being inflexed, the cotyloid cavity for 
2 E 2 
